Quote:
No vacuum advance AND a vacuum leak. With that repair you kill two birds with one hose.

Keep that mechnic......tight valves will burn up if not corrected. I always err on the loose side.
Plugged exhaust definetly explains why it wouldn't rev!!!
It doesn't take much to get an engine running way off, it will still run but not well. You should see what 1 degree of dwell to many does to our old Ford truck.
Anyway glad to hear you car is running sweat.

Tom

Hi all

Good news.
I found the problem. I took my car in for a tappet ajustment because one tappet was making a bit of noise for some time.
When I got it back. The mechanic informed me that ALL tappets were too tight and one was too loose.
He ajusted them correctly. (This is the mechanic who helped a Datsun racing team in the early 80's. They raced a 1200GX).

I also discovered that my tappet cover breater pipe was blocked due to a sharp bend that made the pipe colapse and shut if off. I replaced this pipe. And very important. I went to a exhaust shop to put on a 2" freeflow exhaust as mine started to make some strange noises from the box.

Through investigation, the exhaust box that was removed was starting to cause blockage inside making it difficult for the car to breath. The engine made alot of noise when revved hard past 5000rpm and it also struggled to rev to 6000rpm.

The results.
Car is now as silent as a mouse.
I can rev it to 6500rpm without noise coming from the engine asif someone is strangling it. And it is much smoother than it was.
I cannot believe that such stupid stuff could have caused the problem.

I also discovered that the vacuum advance pipe was cracked near the distributor.
So bad that I doubt there was any vacuum advance taking place. This pipe I have replaced and must still test if it is going to make a difference.
Does vacuum advance make a big difference?

Quote:

No, at 120 or even 140km/h there is no noticable vibrations. Nice and smooth.
At 140kmh the exhaust is just really making alot of noise.
I think it is because there is now lots of road noise and road vibrations that cancel out the engine.
But like in a drag race situation when you drive it hard in first and second gear the car is low in speed so vibrations from engine are picked up easily.

hi
welcome~

seems like most A series engine have same behavior.. :)

well, good luck for your balancing, hope can see a smooth high-revving engine come out soon. :)
plz share with us what your mech do to balance up the engine. really appreciate that

ya.. travle at near 140kph really vibrate a lot...
well i do that maybe once or twice a month when i goes back to my parents place. (medium long journey). but i belive dats are very reliable.. :)

sam1741

Thanks for your reply.
I am happy that I am not the only one having this problem. I think it is that in the 70's technology was not so good as today.
Most of the people on this site have mixed new technology with old (Balancing all rotating parts of their A series engines).

I will take it to my mechanic to hear what he has to say. He was a Datsun mechanic for a private Datsun racing team in the 70's.
They raced a 1200GX and I think he will know what it is.
But as mentioned, if I want to rev it hard in the future, I wil have to consider a full balance on the engine.
I just hope it will not cause damage if I continue like this. An example is driving it on the freeway at 120 to 140km/h.
This is where the revs are at 4000 to 4500rpm.
At 120 to 140km/h you cannot notice the vibrations.Just hear the exhaust.
But in 1st and second gear where the speed of the car is still low it can be noticed.

hey 1200GXman,

my engine behave just like what u describe~!!
(both A12 and A15)

from idle to 3k rpm.. very smooth
3.5k and above start vibrate..

dono if all A series behave like that....

Quote:

ocphangaz

I will be very very happy if you would inform me when yours is done. I am very interested in before and after comment.
This will tell if I will do mine also or not.
The reason why I do not really want to do it is the money involved. I will have to remove the engine again and might aswell bore it one oversize then. It was already reconditioned about 50 000km ago.
My fianc

stock engines are not balanced... i have the same problems at 4500... most of the people here have street tuned engine mostly are tuned to run above 5000rpms

stock engines like yours and mine are not meant to run that high.. the max hp is at just 5200rpm on stock A12 (compared to current 6400rpms on modern cars)

i'm going to do balancing on my engine. i'll tell you how it goes.

i heard A15 doesn't comes with harmonic balancers... can someone enlightened me?

Quote:

Sorry guys.
It was in total 2mm that was removed.
The step was only 1mm everytime and not 2mm.